1. Field of the Invention
This invention relates to an apparatus for skew correction in cut-sheet paper feeding used in an office equipment such as optical scanner, printer, copier and the like.
2. Description of the Prior Art
In various office machines that use cut-sheet paper feeding such as scanner, printer and copier, a stack of cut-sheet paper is usually placed in a paper tray. A paper pickup mechanism is employed to pick up a top sheet paper and feeds the paper into a paper passage formed between a drive roller and a paper guide. At the end of the paper passage, the drive roller and a pinch roller drive the paper to a working station for operation desired, e.g., scanning, printing, copying, or etc. During the paper being picked up and moved in the paper passage and being driven to the working station, the paper has to make frictional contact with a lot of mechanical means, such as the roller, paper guide, and machine casing. These mechanical means have different degree of friction force because of material property and wearing after long time of use. Paper property and conditions also will affect the friction force level. In addition, inappropriate operation of when stacking the sheet paper into the paper tray will also result in inappropriate alignment of sheet paper. Therefore after a sheet of paper travelling a long way and reaching the working station, the paper could become skew and not being aligned properly, and resulting in poor output quality. A severely skewed paper could also cause paper jam in the machine. Then the machine operation has to stop. It takes times and labor to fix such a problem. Worse, such an event takes place repetitively.
A low price office machine generally includes a movable side board in the paper tray to align paper feeding into the machine. However once the paper enters into the machine and moves along the paper passage before reaching the working station, there is no skew correction means. Some relatively high price office machine has included skew correction means for such purpose. U.S. Pat. No. 5,427,462 discloses such a method for printer. It includes a microprocessor controlled drive roller and a pinch roller that can rotate in reverse to make paper jiggling and dancing on its own weight so that skew leading edge may be made parallel to the roller before feeding for printing. It not only involves a complicated structure (e.g., a microprocessor for controlling the drive roller to rotate forward or backward, a depending plate with fingers to engage the paper, etc.) which needs additional space to accommodate those additional control means, but also the paper input is limited to upper feeding at about sixty degrees from horizontal to create paper jiggling needed, and is expensive to produce. All of this has restricted its applicability.